1. Field of the Invention
The present invention relates to an air conditioner and a method for operating the air conditioner in a cooling mode, and more particularly to an air conditioner in which operating modes of compressors are changed when a cooling load to be eliminated is large and a method for operating the air conditioner in a cooling mode.
2. Description of the Related Art
Generally, an air conditioner is an appliance for cooling or heating a room using a refrigerating cycle of a refrigerant compressed into a high-temperature and high-pressure state by compressors.
FIG. 1 is a schematic view of a conventional air conditioner.
As shown in FIG. 1, the conventional air conditioner comprises an indoor heat exchanger 2 for heat-exchanging air in a room with a refrigerant, thereby cooling or heating the room, an outdoor heat exchanger 4 serving as a condenser for condensing the refrigerant when the indoor heat exchanger 2 functions as a cooler, while serving as an evaporator for evaporating the refrigerant when the indoor heat exchanger 2 functions as a heater, a compressor 6 for compressing the refrigerant from a low-temperature and low-pressure gaseous state into a high-temperature and high-pressure gaseous state in order to supply the high-temperature and high-pressure gaseous refrigerant to the indoor heat exchanger 2 or outdoor heat exchanger 4, an expansion device 8 arranged between the indoor heat exchanger 2 and the outdoor heat exchanger 4 and adapted to expand the refrigerant into a low-temperature and low-pressure state, an operating panel 12 for allowing a user to manipulate the operation of the air conditioner, a temperature sensor 14 for sensing a room temperature, and a control unit 16 for controlling operation of the compressor 6 in response to the manipulation of the user and in accordance with an indoor cooling or heating load to be eliminated. The indoor heat exchanger 2, the outdoor heat exchanger 4, the compressor 6, and the expansion device 8 are connected by a refrigerant pipe 9.
The reference numeral 24 denotes a common accumulator to which a suction line 6a of the compressor 6 is connected. This common accumulator 24 serves to store the refrigerant in a liquid state not evaporated by the indoor heat exchanger 2 or outdoor heat exchanger 4, in order to prevent the liquid refrigerant from being introduced into the compressor 6. Introduction of such a liquid refrigerant into the compressor 6 may cause failure of the compressor 6.
Also, the reference numeral 26 denotes a direction change valve, for example, a 4-way valve, adapted to change the flow direction of the refrigerant in accordance with a control signal from the control unit 16 so that the air conditioner is used for a cooling or heating purpose. This 4-way valve 26 communicates with the common accumulator 24 and a discharge line 6b of the compressor 6. The 4-way valve 26 guides the high-temperature and high-pressure gaseous refrigerant compressed by the compressor 6 to the outdoor heat exchanger 4 in a cooling mode, while it guides the same gaseous refrigerant to the indoor heat exchanger 2 in a heating mode.
Now, a method for operating the above-described conventional air conditioner in the cooling mode will be described in detail.
First, the air conditioner is set to be operated in a cooling mode under the condition in which a target temperature T0 is set, and the control unit 16 switches the operating position of the 4-way valve 26 to correspond to the cooling mode, as shown in FIG. 1.
The control unit 16 compares a room temperature sensed by the temperature sensor 14 with the target temperature T0 set by a user via the operating panel 12. When the room temperature is not lower than the target temperature T0, the control unit 16 operates the compressor 6. When the room temperature is lower than the target temperature T0, the control unit 16 stops the operation of the compressor 6.
When the compressor 6 is operated, the compressor 6 discharges a high-temperature and high-pressure gaseous refrigerant to the outdoor heat exchanger 4. When the refrigerant passes through the outdoor heat exchanger 4, the refrigerant is heat-exchanged with the peripheral air, thereby radiating heat and then being condensed into a high-temperature and high-pressure liquid state. Then, the condensed refrigerant in the high-temperature and high-pressure liquid state passes through the expansion device 8, thereby being expanded into a low-temperature and low-pressure state inducing evaporation. When the expanded refrigerant passes through the indoor heat exchanger 2, the refrigerant is heat-exchanged with indoor air, thereby absorbing heat and then being evaporated. Then, the refrigerant is introduced again into the compressor 6. Thereby, a cooling cycle is established.
Recently, in order to meet a trend towards large scale and multi-function applications, air conditioners have been developed to comprise two or more compressors. The total capacity of the plural compressors is variably changed in accordance with a cooling or heating load in a room to be eliminated. Accordingly, it is possible to reduce power consumption required to operate the plural compressors and to rapidly cope with the variation of the cooling or heating load.
Since the earlier conventional air conditioner in a cooling mode operates a single compressor 6 and stops the operation of the compressor 6 by comparing a room temperature with a target temperature. Further, since the recently developed air conditioner comprising the plural compressors operates the plural compressors simultaneously and stops the operation of the plural compressors simultaneously even when a cooling load in a room to be eliminated is small, it is difficult to reduce an electric power consumption rate.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an air conditioner for reducing an electric power consumption rate and a method for operating the air conditioner in a cooling mode.
It is another object of the present invention to provide a method for operating an air conditioner in a cooling mode, which rapidly copes with the requirements of a user.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an air conditioner comprising: small-capacity and large-capacity compressors for compressing a refrigerant; a temperature sensor for sensing a room temperature; an operating panel for allowing a user to manipulate the air conditioner and to input a target temperature therethrough; and a control unit for determining a cooling load in a room to be eliminated by comparing the room temperature sensed by the temperature sensor with upper and lower temperature limits being higher and lower than the target temperature by an allowable deviation, and for controlling an independent or simultaneous operation of the small-capacity and large-capacity compressors so that the room temperature is maintained in the range of the upper and lower temperature limits when it is determined that the cooling load is large.
In accordance with another aspect of the present invention, there is provided a method for operating an air conditioner in a cooling mode for cooling air in a room by an independent or simultaneous operation of small-capacity and large-capacity compressors in accordance with the variation of a cooling load, comprising the steps of: (a) operating the small-capacity compressor; (b) stopping the operation of the small-capacity compressor and operating the large-capacity compressor when it is determined that the room temperature is higher than a first set temperature after the lapse of a first predetermined time after the small-capacity compressor is operated at the step (a); and (c) re-operating the small-capacity compressor together with the operation of the large-capacity compressor when it is determined that the room temperature is higher than a second set temperature after the lapse of a second predetermined time after the large-capacity compressor is operated at the step (b).